Hien was the Vice-Chief of [Rokkaku] under Hanzo. He was born as a "high caste ninja," and for that reason was allowed to become the Vice-Chief. He was a highly competent ninja, and trained Kasumi and Sasuke before Mondo took over the task of their training. When Teo McDohl attacked [Rokkaku] under the order of Barbarossa, Hien stalled Teo while the rest of the ninjas escaped. Hien lost his life in the process. Only Hanzo and Mondo know that Hien is the father of Sasuke. It is a custom in [Rokkaku] for high caste ninjas to be raised separate from their parents to force them a life of self-reliance. - Blue Moon